I found the magic cake via Pinterest: "recipe for magic cake: one dough forms three layers while baking and tastes like vanilla custard" pinned from Zuckerzimtundliebe. If that doesn't scream witchery, I don't know. So straight in the kitchen and "Hey presto"!

Preheat the oven to 160°C, butter a leakproof baking dish (20x20 cm) and optionally line it with parchment paper.

Melt the butter and warm the milk, they should both be lukewarm, don't get it too hot.

Separate the eggs and beat the egg whites until firm. Mix the egg yolks with the icing sugar until creamy, add butter and water and continue mixing for about 2-3 minutes. Add the flour and cinnamon and mix well. Slowly pour the milk in (it could splatter!) and mix until incorporated. The dough is very liquid. Stir in one third of the beaten egg whites, fold in the second third until no big egg white islands remain, then carefully fold in the last third. Don't overmix! Pour the batter immediately into the baking dish and bake for about 50-60 minutes. The top should be golden brown and the middle slightly wobbly (like cheese cake).

This cake really tastes like vanilla custard although there is no vanilla in it.

I thought it wouldn't work while preparing the batter but everything was fine and everybody loved it. However, my cake formed a big bladder ( you can see it on the second pic in the background), but it deflated after baking.